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12v to 220v inverter design

Discussion in 'General Electronics Discussion' started by danish raza, Jun 5, 2011.

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  1. danish raza

    danish raza

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    Jun 5, 2011
    hello every one!
    i am building inverter of approx 300w i am using pic16f877a for driving the mosfet...my question is that i am using stp75nf75 mosfet..as stp75nf75 requires VGS=10v to get fully on so i am using optocoupler for providing 10v and controlling optocoupler through pic can anyone suggest me that the mosfet which i am using will be fine or any other suitable mosfet can be used to make the inverter work .
     
    Last edited: Jun 5, 2011
  2. danish raza

    danish raza

    8
    0
    Jun 5, 2011
    need help in inverter

    hello every one!
    i am building inverter of approx 300w i am using pic16f877a for driving the mosfet...my question is that i am using stp75nf75 mosfet..as stp75nf75 requires VGS=10v to get fully on so i am using optocoupler for providing 10v and controlling optocoupler through pic can anyone suggest me that the mosfet which i am using will be fine or any other suitable mosfet can be used to make the inverter work .
     
  3. duke37

    duke37

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    Jan 9, 2011
    You do not say how the optocoupler will be used, it seems that you are complicating things.
    If the frequency is constant then a CMOS 4047 oscillator can be used to drive the mosfet(s) and will run on 10V.
    A transistor with a collector resistor going to 10V will also do the job if you insist on a pic. Optocouplers are used when there is not a common ground connection.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    If I were you I would be looking at a mosfet driver to drive the gate of the mosfet. If you need the electrical isolation, you can retain the optocoupler, otherwise it may be possible to remove it.

    A mosfet gate driver will allow high gate currents, thus ensuring fast switching and consequently low switching losses in the mosfet.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Please don't start multiple threads for the same issue raza. It just gets you offside with the moderators.
     
  6. danish raza

    danish raza

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    Jun 5, 2011
    12v to 220v

    hy every one,
    i had made an inverter the problem is that at the output of transformer the voltage is 160 to 170v but i required 220v..i want to stepp up from 12 v to 220v using center tapped transformer but it does not happening i am receiving only 160 to 170 v kindly guide me and i am using the battery of 12v and 9A ?
     
  7. duke37

    duke37

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    Jan 9, 2011
    It appears that the transformer is wrong. What transformer are you using? Is it a 12V transformer used in reverse?
    If you get a 220V to 12V transformer, there will be extra turns on the secondary to compensate for resistive loss when under load. The turns ratio may be 10% out. If this transformer is used in reverse, you will get 10% less voltage than you might think. This will drop further under load.
    There is also the question of the waveform and how the voltage is measured.
    Also, does the battery give 12V under load?
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    OK, also consider 220V RMS.

    220VAC is typically 220V RMS, which means that the voltage goes from -311 to +311 volts, but if you passed it through a resistor (think bar heater) it would produce the same heating effect as 220V DC.

    Now if you are using a 12V battery to drive a 12V to 220V transformer (via some means of creating AC) then you are almost certainly supplying a voltage which varies from -12V to +12V to the secondary. Now whilst this may actually have an RMS voltage of 12V (the conversion to RMS depends on the "shape" of the waveform), limitations of the transformer will make it appear more like 8.5V RMS. When you apply 8.5V to a 12V winding, the 220V winding will have 155V appearing on it. And that's pretty close to the 160 to 170 you're seeing.

    This may not be the case, but it's certainly a possibility for which the numbers "work".
     
  9. danish raza

    danish raza

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    Jun 5, 2011
    so can you guide me how to overcome this problem?
     
  10. davenn

    davenn Moderator

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    Sep 5, 2009
    it mite help us if we saw your circuit. Maybe we can see some problems with the design that changes can be suggested :)

    Otherwise we are just guessing in the dark


    Dave
     
  11. danish raza

    danish raza

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    Jun 5, 2011
  12. danish raza

    danish raza

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    Jun 5, 2011
    i am using 12+12v center tapped transformer yes the battery is giving 12 v
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    He does recommend a 20V CT transformer, not a 24V CT transformer. I suspect that getting the transformer as specified will give you performance closer to specified.
     
  14. davenn

    davenn Moderator

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    Sep 5, 2009
    and what is the VA rating of the transformer you are using?
    hopefully at least 110VA (Watts)


    Dave
     
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